I don't think this system is searchable. You'll be storing a bunch of encrypted blobs, each of which can be retrieved and decrypted by anyone who knows a short key. One of them might be a CP picture (if you store enough of them, statistically one of them will be a CP picture). One of them might be an index full of other short keys, pointing to a whole host of CP pictures spread across the mesh.
If you're fine with that, that's good enough; you can run this system, and political activists and perverts alike will be able to stick their blocks there, accessible to anyone to whom they can pass the relevant short keys. But many people will be uncomfortable with even this much.
Yeah this system does not appear to be the quick glance I looked, but api's disired system does not need to model this one.
> How do we design a system that is anonymous and un-censorable where users can opt out of being relays for certain types of data?
As long as we are reasonable by taking "un-censorable" to mean very difficult to censor and "users can opt out of certain types of data" to mean highly limit traffic of data type <x>, it seems like a hard problem until proven impossible.
It's (AIUI) meant as a replacement for pastebin etc. - you host something on this mesh, and then you only have to spread a short hash key around. It also lets you do the wikileaks thing of publishing a bunch of encrypted data which you could later release the key to.